For preventing infectious diseases such as hepatitis B, there has generally been used a method of administering immunoglobulins formed in blood plasma against a target antigen. However, the method has the problems that the immunoglobulins generally have low specificity and may contain contaminants.
Murine monoclonal antibody derived from mouse has been reported to have high affinity to antigen and is suitable for mass-production. However, repeated injection of murine monoclonal antibody induces an immune response because the murine antibody is regarded as a foreign antigen in humans (Shawler D. L. et al., J. Immunol., 135, 1530-1535(1985)).
Accordingly, numerous efforts have been made to generate “humanized antibody” by: grafting the CDR (complementarity determining region) of murine monoclonal antibody variable region which directly binds to antigens, to a human antibody framwork (CDR-grafting method); and replacing the amino acid residues of the human antibody framework region (FR) that influence the CDR conformation with the amino acid residues of murine monoclonal antibody. The humanized antibody thus obtained maintains the affinity and specificity of original murine monoclonal antibody, and minimizes HAMA(human anti-mouse antibody) response in humans (Riechmann et al., Nature, 332, 323-327(1988); Queen C. et al., Proc. Natl. Acad. Sci. USA, 86, 10029-10033(1989); Nakatani et al., Protein Engineering, 7, 435-443(1994)). However, this humanized antibody still causes problems when injected repeatedly into humans (Stephens et al., Immunology, 85, 668-674(1995); Sharkey et al., Cancer Research, 55, 5935s-5945s(1995)).
Approximately 300 millions of world population carry hepatitis B virus (“HBV”) which may cause chronic infection, leading to cirrhosis and hepatocellular carcinoma (Tiollais P. and Buendia M. A., Sci. Am., 264, 48(1991)). The HBV envelope consists of three proteins, major protein containing S antigen, middle protein containing S and pre-S2 antigens, and large protein containing S, pre-S2 and pre-S1 antigens (Neurath A. R. and Kent S. B., Adv. Vir. Res., 34, 65-142(1988)). These surface antigens have been known to play important roles in the process of forming antibodies against HBV in hepatitis patient. The pre-S1 region, in particular, is found on infectious viral particles (Heermann et al., J. Virol., 52, 396-402(1984)) and plays a role in attachment to cell surface infection (Neurath et al., Cell, 46, 429(1986); Pontisso et al., Virol., 173, 533, (1989); Neurath et al., Vaccine, 7, 234(1989)). Thus a monoclonal antibody against the pre-S1 would be effective against viral infection.
The present inventors have previously reported a murine monoclonal antibody (KR127) against HBV pre-S1 (Korean Patent No. 246128), a murine monoclonal antibody KR127 gene encoding same (Korean Patent No. 250832) and a humanized antibody (HZKP127I) of KR127 prepared by CDR-grafting method (Korean Patent No. 246128).
The present inventors have further endeavored to develop a humanized antibody having minimized adverse immune response (HAMA response) as well as enhanced affinity to antigen, and found that HAMA response can be reduced when the amino acid residues of CDR of mouse antibody are replaced with those of human antibody.